Biliary, pancreatic and hilar ducts may become occluded when biliary, pancreatic, or hepatic cancer invades the duct or an external cancer mass compresses and blocks the ducts. Cholangiocarcinomas are malignancies of the biliary duct system that start in the liver or extra-hepatic biliary ducts. They can start in one of the ducts and invade and extend to the ampulla of Vater.
These malignancies have a very high morbidity and mortality rate. As an example, pancreatic cancer patients have a life span that is measured in months after diagnosis, often after extensive invasive treatments and chemotherapy. This high mortality is due to the rapid progression of the cancer resulting in complications that are often the cause of the patient's demise. The complications of pancreatic cancer include ductal occlusion with biliary flow obstructions resulting in jaundice and encephalopathy, ascending cholangitis and rapid death from sepsis, very severe pain that is difficult to control, even with high dose opioids that results in medication-induced sedation, cachexia and wasting, and many other complications.
The issues that occur in ductal obstruction and occlusion are unique to the biliary system due to the “harsh environment” of the biliary drainage system as pancreatic and biliary enzymes and the “dirty environment” with the fungi and bacteria that inhabit the ducts make stasis and injury to these ducts susceptible to complete occlusion by biofilm (bacteria) and organic masses (‘fungal balls’). In addition, bleeding of the ducts, with or without stent placement can cause clot formation and occlusion. Invasion by the tumor within the ductal wall and occlusion of the duct by external compression by a tumor mass are also common causes of complications.
Treatment of ductal occlusion has been partially addressed with stainless steel stents, cobalt chromium stents, inexpensive plastic stents and, more recently, shape memory alloy stents. These stents are placed in a harsh enzymatic environment and re-occlusion occurs frequently. If the patient survives a month or months, a stent-in-stent can be performed but often times the complications described above result in the terminal state before this can be performed.
One problem with many different types of implants, and, in particular, biliary stents, is migration of the implant or stent from the desired location. Once the stent migrates, the bile duct closes. This, of course, can be a problem with other stents, as well as implants of various sizes and shapes.
Frequently, it is desirable to place a tubular implant, such as a stent, at the point at which the biliary duct enters the duodenum. This particular opening widens as the biliary duct approaches the duodenum. As a result, the desired shape of an implant would be frustoconical, but such an implant inherently tends to migrate.